Process for spinning and drawing polyalkylene isophthalamides



May 7; 1963 DRAWN l l l l I vvVV 79' lameml BOILED OFF IN H20 United States Patent 3,088,794 PROCESS FUR SPINNING AND DRAWING POLYALKYLENE ISOPHTHALAMIDES Willard Hallam Bonner, Jr., Wilmington, Del., assignor to E. I. du Pont de Nemours and Company, Wilmington,

DeL, a corporation of Delaware Filed Aug. 26, 1960, Ser. No. 52,028 4 Claims. (Cl. 13-54) This invention relates generally to synthetic polyamide yarns and, more particularly, to the preparation of useful polyalkylene isophthalamide yarns.

Polyhexamethylene isophthalamide and polytetramethylene isophthalamide are known in the art. However, when conventional spinning and drawing processes are applied to these polymers, an amorphous, non-oriented yarn having very poor properties results. Prior attempts to introduced both crystallization and orientation :have failed.

It is an object of this invention to provide polyhexamethylene isophthalamide and polytetramethylene isophthalamide yarns having improved tensile properties, in particular, a higher modulus and tenacity. A further important object is to provide process improvements useful in the preparation of such yarns.

A specific object is the provision of a process for converting a non-crystalline, unoriented, as-spun polyhexamethylene isophthalamide or polytetramethylene isophthalamide yarn into a crystalline, oriented, drawn yarn.

With these and other objects in view, a crystalline and oriented polyhexamethylene isophthalamide or polytetramethylene isophthalamide yarn is provided by spinning the isophthalamide into an amorphous, unoriented asspun yarn, treating the as-spun yarn in a crystallization agent, and drawing the crystallized yarn to obtain a crystalline, oriented yarn. The yarn may then be boiled-ofi to further enhance its properties. The starting polymer may be prepared by interface polymerization or by melt polymerization, and the yarn may either be dry spun or melt spun.

In principle, the drawing step may be carried out at any temperature between room temperature and the melting point of the polyalkylene isophthalamide but, in practice, a temperature between about 160 C. and about 200 C. is preferred. The preferred temperature range varies somewhat with the individual polymer. For polyhexamethylene isophthalamide, the preferred range is from about 160 C. to about 190 C. [For polytetramethylene isophthalamide, the preferred temperature range is from about 185 C. to about 200 C.

The boil-off step is accomplished by immersing the drawn yarn on a bobbin in taut form, with the ends tied together, in boiling water for 5 minutes or longer. About 15 minutes is convenient.

The crystallization agent may be a liquid mixture or swelling agent that penetrates but does not dissolve the yarn. Suitable liquid agents are, for example, an aqueour solution of formic acid (SO-90% water), an aqueous solution of dimethylformamide (5090% water), an aqueous solution of acetic acid (50% water), methanol or water. In addition to the above and other swelling agents, the crystallization agent may also be steam, hot air, hot nitrogen, or other forms of heat.

When a liquid swelling agent is used, the treatment must be such as to insure that the liquid penetrates the yarn. The time required depends on the temperature employed. About two minutes is usually suflicient and at least six minutes is preferred. This treatment may consist of immersing the yarn wound taut on a bobbin into a bath containing the liquid agent, immersing the yarn relaxed in skein form, or passing the yarn through the bath by means of rollers When steam, hot air or nitrogen are em- 3,088,794 Patented May 7, 1963 ployed as the crystallizing agent, the time of treatment will depend on the temperature employed. Using steam at C., this time is approximately 5 minutes. Using nitrogen gas in the preferred temperature range of 200 C., the time required is at least 30 minutes and preferably from 2-3 hours. The steam, hot air, hot nitrogen, or the like, can be applied to the yarn when it is taut on a bobbin or relaxed in skein form, or by passing the yarn through the exposure zone on rolls.

In the appended drawing, the soaking, drawing and boiloff steps described in Example I have been shown schematically. As illustrated, the yarn is wound taut on a bobbin, with the ends tied together, during the soaking and boil-off steps.

The crystallinity index recorded in the examples is measured according to the procedure described by Wakelin, Virgin, and Crystal in J. Appl. Phys, 30, 1654 (1959). In this procedure, the most crystalline polymer sample obtainable is given a value of 100 and the least crystalline sample a value of zero. The index for the various fiber samples is thus a relative measure of crystallinity between these two known extremes. To obtain the zero index for the polymers disclosed herein, the latter were spun into fibers which were amorphous to X-rays. To obtain the 100 index, a melt-pressed film was allowed to soak in an aqueous 50% dimethylformamide solution for ten minutes and then thermally annealed for six hours at 200 C.

The orientation in the crystalline regions can be measured by the procedure of H. G. Ingersoll which is discussed in J. Appl. Phys, 17, 924 (1946). As reported herein a low orientation angle is indicative of high orientation in the crystalline regions.

A recognized parameter for measuring total orientation is the percent molecular orientation at break elongation. This roperty has been described by W. H. Charch and W. W. Moseley in the Textile Research Journal, vol. XXIX, p. 525 (1959).

As noted previously, the properties of the yarn are further enhanced by following the crystallizing and drawing steps with a boil-off step. The crystallinity index of polyhexamethylene iso-phthalamide yarn may be raised further by following the boil-01f taut treatment with a heat treatment at about C. at a tension that permits a slight retraction, for 5 to 10 minutes (Example IV).

Yarns prepared according to the teachings of the present invention find a useful application in the fabrication of the cords as well as in carpets and apparel end uses. Their preparation and characterization are described in greater detail in the following examples.

EXAMPLE I To a 1-liter Waring Blendor under nitrogen is added a solution. of 23.2 g. (0.2 mole) of distilled hexamethylenediamine (handled during weighing in a nitrogen atmosphere) in 200 ml. of distilled water. To this solution is added rapidly, with high speed stirring, a solution of 20.3 g. (0.1 mole) of pure isophthalyl chloride in 200 ml. of methylene chloride. The solid, white polyhexamethylene isophthalamide precipitates out of solution immediately as a large, solid mass and stirring becomes ineflective after about 15 seconds. The solid product is removed from the Blendor and soaked in acetone for several minutes, after which time it is again placed in the Blendor with approximately 500 ml. of acetone and cut up into small pieces resembling strips of wood shavings by the rapid stirring action of the Blendor blades. The resulting product is then washed in the Blendor with two 500 portions of distilled water, once more with acetone and then dried in a vacuum oven at 100 C. for about 5 hours to give roughly 17-18 g. of polyhexa- 3 methylene isophthalamid'e having an inherent viscosity in meta-cresol of 1.4.

About 40 g. of polymen'prepared by interface polymerization as described. above, is dissolved in a solvent containing 50% by weight of freshly distilled trichloroethane, 49% formic acid and about 1% Water to give a spinning dope containing 20% solids. Polyhexamethylene isophthalamide yarn is obtained from such a dope by the dry spinning technique using a column temperature of about 180-190 C. to evaporate the solvent. The yarn is plied to 20 filaments and dried by standing in an exhaust hood.

The as-spun yarn is then wound on a bobbin and soaked taut, with the ends tied together as illustrated, in a 50% solution of dimethylformamide in Water at the preferred temperature of 55 C. for 6 minutes to induce crystallization. The crystalline yarn is drawn at a draw ratio of 5.0 over a plate at 170 C. The drawn yarn is boiled oif taut, with the ends tied together as illustrated, in Water at 100 C. for 30 minutes. The orientation angle, crystallinity index, and percent molecular orientation of the yarn are measuredas Well as the tenacity, break elongation and initial modulus. Similar Values for a control yarn, which was not treated with a crystallizing agent, are included in the following table for purposes of comparison. The experiment was repeated, omitting the boil-01f, and these results also are recorded in the table.

To a 1 liter Waring Blender under nitrogen is added a solution of,17.6=g. (0.2 mole") of distilled tetramethylenediamine (handled during weighing in a nitrogen atmosphere) in 200ml. of distilled water. To this soluis added rapidly, with high speed stirring, a solution of 20.3 g'. (0.1 mole) of pure isophth alyl chloride in ,200 fill-f methylene chloride. Thesolid, white polytetrameth'ylene isophthalamide precipitates ou of solution after 15 seconds as a large, solid mass and stirring continued another- 2 minutes. The solid product is removed from the Blender and soaked in acetone for several minutes, after which time it is broken by hand into small pieces and washed in the Blendor with water, acetone (two times) and water. After drying in a vacuum at 100 C. for 5 hours, 16. g. (73%) of white polytetramethylene i-sophthalamide are obtained. The inherent viscosity. in meta cresol is 1.5.

.About 40 g. of the polymer, prepared. as described above, is dissolved in a solvent containing 40% by weight of freshly distilled trichloroeth-ane and 60% formic acid to give a spinning dope containing 23% solids. Polytetramethyleneisophthalamide yarn is obtained from such a dope by the dry spinning technique; using a column temperature of about 180-190 C. to evaporate thesolvent. The yarn is plied to 20 filaments and dried by standing in an exhaust hood.

The as-spun yarn is then wound on a bobbin and soaked taut, with the ends tied together, in boiling water for 30 minutes to induce crystallization. The crystalline yarn is drawn at a ratio of 5 .0 over a pin at 195 C. The drawn yarn is boiled off taut in water at C. for 30 minutes. The T/E/M values are 2.0/ 10/ 6 3.

EXAMPLE III Polyhexamethylene isophthalamide' is prepared as follows: hexamethylene diammonium isophthalate salt in a methanol solution, pH 7.45, was heated with 0.2% boric acid for one hour at 231 C. under a nitrogen atmosphere, followed by a two-hour nitrogen cycle at 265 C. and a one-half hour vacuum cycle (0.5 mm.), also at 265 C. A pale yellow polymer having an inherent viscosity of 1.2-1.3 in meta-cresol is obtained and melt spun in a melt extruder at 340 C., 1,200 p=.s.i., into a 5 filament total denier yarn at a spinning speed of 40 yards per minute. The as-spun yarn is crystallized and drawn according to the techniques of Example I and yarn with properties similar to those reported in the table is obtained.

EXAMPLE IV A crystallin oriented polyhexarnethylene isophthalamide yarn is prepared following the procedure of Exampie 1. It is further crystallized by annealing at 195 C. for ten minutes under conditions which permit a slight retraction. These conditions are realized by wrapping the yarn sample around an X-ray camera yarn holder. Upon annealing the crystallinity index has increased from 60 to 80. The orientation has decreased somewhat as judged from the increase in orientation angle from 14 to 20.

Having thus described the invention, what is claimed as new and desired to be secured by Letters Patent is:

1. A process comprising the steps of: spining yarn from a polymer taken from the group consisting of polyhexamethylene isophthalamide and polytetramethylene isophthalamide; treating the as-spun yarn, in a taut condition, by soaking in an aqueous solution of dimethyl formarnide; and drawing the treated yarn over a heated draw element.

2. The process of claim 1 wherein the solution is at about 55 C. and the duration of the treating step, is in excess of two minutes and sufficient to penetrate the as-spun yarn.

3. The process of claim 2 wherein the drawn yarn is held taut and boiled-01f by immersion in boiling water.

4. A process comprising the steps of: spinning yarn from polyhexamethylene isophthalamide; treating the asspun yarn, in a taut condition, by soaking in an aqueous solutionofdimethyl formamide at about 55 C. for a period sufiicient to penetrate the yarn; drawing the treated yarn over a draw element heated to a temperature of from -190" C.; and boiling-01f the drawn yarn by immersion in boiling water.

References Cited in the file of this patent UNITED STATES PATENTS 

1. A PROCESS COMPRISING THE STEPS OF: SPINING YARN FROM A POLYMER TAKEN FROM THE GROUP CONSISTING OF POLYHEXAMETHYLENE ISOPHTHALAMIDE AND POLYTETRAMETHYLENE ISOPHALAMIDE; TREATING THE AS-SPUN YARN, IN A TAUT CONDITION, BY SOAKING IN AN AQUEOUS SOLUTION OF DIMETHYL FORMAMIDE; AND DRAWING THE TREATED YARN OVER A HEATED DRAW ELEMENT. 